U.S. patent application number 10/824772 was filed with the patent office on 2005-01-06 for dithiolene functionalized polymer membrane for olefin/paraffin separation.
Invention is credited to Burns, Ryan L., Koros, William J..
Application Number | 20050000899 10/824772 |
Document ID | / |
Family ID | 32908750 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050000899 |
Kind Code |
A1 |
Koros, William J. ; et
al. |
January 6, 2005 |
Dithiolene functionalized polymer membrane for olefin/paraffin
separation
Abstract
A polymeric composite may be used for forming fluid separation
membranes. The membranes may be formed from polyimide, polyamide or
poly (pyrrolone-imide) materials. Polyamides may be formed by the
condensation of a tetraamine, a tetraacid, and a diamine.
Polyimides and poly (pyrrolone-imides) may be formed by the
cyclization of a polymer precursor. A polymeric composite may
include a dithiolene or a mixture of dithiolenes. A polymer matrix
incorporating dithiolenes may exhibit an olefin/paraffin solubility
selectivity. A solubility selectivity may be between about 1.1 and
about 2.0.
Inventors: |
Koros, William J.; (Atlanta,
GA) ; Burns, Ryan L.; (Yorktown Heights, NY) |
Correspondence
Address: |
MEYERTONS, HOOD, KIVLIN, KOWERT & GOETZEL, P.C.
P.O. BOX 398
AUSTIN
TX
78767-0398
US
|
Family ID: |
32908750 |
Appl. No.: |
10/824772 |
Filed: |
April 15, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60463008 |
Apr 15, 2003 |
|
|
|
Current U.S.
Class: |
210/650 ;
210/500.27; 210/500.38; 210/500.39 |
Current CPC
Class: |
B01D 67/0011 20130101;
B01D 53/228 20130101; B01D 71/56 20130101; B01D 69/142 20130101;
C07C 7/144 20130101; B01D 71/62 20130101; C07C 7/144 20130101; B01D
2257/7022 20130101; B01D 69/12 20130101; B01D 71/64 20130101; B01D
2325/022 20130101; C07C 11/02 20130101 |
Class at
Publication: |
210/650 ;
210/500.27; 210/500.38; 210/500.39 |
International
Class: |
B01D 061/00 |
Claims
1. A fluid separation membrane for separating one or more
components from a fluid, the fluid comprising two or more
components, wherein the fluid separation membrane comprises at
least one polymer and at least one dithiolene having the structure:
27where M is a metal, wherein R.sub.1, R.sub.2, R.sub.3, and
R.sub.4 are each independently alkyl, CH.sub.3, CF.sub.3,
C.sub.6H.sub.4OCH.sub.3, CN, or where R.sub.1 and R.sub.2 and/or
R.sub.3 and R.sub.4 combine to form at least one ring.
2. The fluid separation membrane of claim 1, wherein the membrane
exhibits an olefin/paraffin solubility selectivity.
3. The fluid separation membrane of claim 1, wherein the membrane
exhibits an olefin/paraffin solubility selectivity of 1.1 to
2.0.
4. The fluid separation membrane of claim 1, wherein at least one
dithiolene is resistant to poisoning by impurities.
5. The fluid separation membrane of claim 1, wherein the metal is
Ni, Pd, or Pt.
6. The fluid separation membrane of claim 1, wherein at least one
dithiolene further comprises a valence charge, and wherein the
valence charge is 0, -1, or -2.
7. The fluid separation membrane of claim 1, wherein at least one
dithiolene further comprises a valence charge, wherein the valence
charge is -1 or -2, and wherein the dithiolene comprises a counter
ion.
8. The fluid separation membrane of claim 1, wherein at least one
dithiolene further comprises a valence charge, wherein the valence
charge is -1 or -2, and wherein the dithiolene comprises at least
one counter ion having the structure: 28where each R is
independently an alkyl or aromatic compound.
9. The fluid separation membrane of claim 1, wherein at least one
dithiolene further comprises a valence charge, wherein the valence
charge is -1 or -2, and wherein the dithiolene comprises at least
one counter ion having the structure: 29where each R is
independently C.sub.2H.sub.5 or C.sub.4H.sub.9.
10. The fluid separation membrane of claim 1, wherein at least one
dithiolene is capable of complexing with an olefin.
11. The fluid separation membrane of claim 1, wherein the fluid
comprises a liquid.
12. The fluid separation membrane of claim 1, wherein the fluid
comprises a gas stream.
13. The fluid separation membrane of claim 1, wherein the fluid
comprises a gas stream, and wherein the gas stream comprises a
hydrocarbon.
14. The fluid separation membrane of claim 1, wherein R.sub.1,
R.sub.2, R.sub.3, and R.sub.4 are CH.sub.3, at least one dithiolene
having the structure: 30
15. The fluid separation membrane of claim 1, wherein R.sub.1,
R.sub.2, R.sub.3, and R.sub.4 are CF.sub.3, at least one dithiolene
having the structure: 31
16. The fluid separation membrane of claim 1, wherein R.sub.1,
R.sub.2, R.sub.3, and R.sub.4 are C.sub.6H.sub.4OCH.sub.3, at least
one dithiolene having the structure: 32
17. The fluid separation membrane of claim 1, wherein R.sub.1 and
R.sub.2 combine to form C.sub.6H.sub.3CH.sub.3, and wherein R.sub.3
and R.sub.4 combine to form C.sub.6H.sub.3CH.sub.3, at least one
dithiolene having the structure: 33where each R is independently H,
CH.sub.3, alky, or aryl.
18. The fluid separation membrane of claim 1, wherein R.sub.1 and
R.sub.2 combine to form C.sub.6H.sub.4S.sub.4, and wherein R.sub.3
and R.sub.4 are CF.sub.3, at least one dithiolene having the
structure: 34
19. The fluid separation membrane of claim 1, wherein at least one
polymer comprises the reaction product of a tetraacid compound and
a diamine.
20. The fluid separation membrane of claim 1, wherein at least one
polymer comprises the reaction product of a tetraacid compound and
a diamine, wherein the tetraacid compound comprises an aromatic
dianhydride having the structure: 35wherein the diamine having the
structure: 36and wherein each X is independently CH.sub.2, C(O),
CH(CH.sub.3), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, C(CH.sub.3)Ph,
C(Ph).sub.2, or cyclohexyl.
21. The fluid separation membrane of claim 1, wherein at least one
polymer comprises a polyimide polymer, a polyamide polymer, a
polypyrrolone polymer, or a poly (pyrrolone-imide) polymer.
22. The fluid separation membrane of claim 1, wherein at least one
polymer comprises a polyimide polymer, wherein the polyimide
polymer comprises recurring units, a portion of the recurring units
having the structure: 37where X is a linking group, and Y is
another recurring unit, where recurring unit Y is coupled to the
aromatic ring in an ortho, meta, or para relation to the imide
group.
23. A fluid separation membrane for separating one or more
components from a fluid, the fluid comprising two or more
components, wherein the fluid separation membrane comprises at
least one polymer and at least one dithiolene having the structure:
38where M is a metal.
24. The fluid separation membrane of claim 23, wherein the membrane
exhibits an olefin/paraffin solubility selectivity.
25. The fluid separation membrane of claim 23, wherein the membrane
exhibits an olefin/paraffin solubility selectivity of 1.1 to
2.0.
26. The fluid separation membrane of claim 23, wherein the metal is
Ni, Pd, or Pt.
27. The fluid separation membrane of claim 23, wherein at least one
dithiolene further comprises a valence charge, and wherein the
valence charge is 0, -1, or -2.
28. The fluid separation membrane of claim 23, wherein at least one
dithiolene further comprises a valence charge, wherein the valence
charge is -1 or -2, and wherein the dithiolene comprises a counter
ion.
29. The fluid separation membrane of claim 23, wherein at least one
dithiolene further comprises a valence charge, wherein the valence
charge is -1 or -2, and wherein the dithiolene comprises at least
one counter ion having the structure: 39where each R is
independently an alkyl or aromatic compound.
30. The fluid separation membrane of claim 23, wherein at least one
dithiolene further comprises a valence charge, wherein the valence
charge is -1 or -2, and wherein the dithiolene comprises at least
one counter ion having the structure: 40where each R is
independently C.sub.2H.sub.5 or C.sub.4H.sub.9.
31. The fluid separation membrane of claim 23, wherein at least one
dithiolene is capable of complexing with an olefin.
32. The fluid separation membrane of claim 23, wherein the fluid
comprises a liquid.
33. The fluid separation membrane of claim 23, wherein the fluid
comprises a gas stream.
34. The fluid separation membrane of claim 23, wherein the fluid
comprises a gas stream, and wherein the gas stream comprises a
hydrocarbon.
35. The fluid separation membrane of claim 23, wherein at least one
polymer comprises the reaction product of a tetraacid compound and
a diamine.
36. The fluid separation membrane of claim 23, wherein at least one
polymer comprises the reaction product of a tetraacid compound and
a diamine, wherein the tetraacid compound comprises an aromatic
dianhydride having the structure: 41wherein the diamine having the
structure: 42and wherein each X is independently CH.sub.2, C(O),
CH(CH.sub.3), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2, C(CH.sub.3)Ph,
C(Ph).sub.2, or cyclohexyl.
37. The fluid separation membrane of claim 23, wherein at least one
polymer comprises a polyimide polymer, a polyamide polymer, a
polypyrrolone polymer, or a poly (pyrrolone-imide) polymer.
38. The fluid separation membrane of claim 23, wherein at least one
polymer comprises a polyimide polymer, wherein the polyimide
polymer comprises recurring units, a portion of the recurring units
having the structure: 43where X is a linking group, and Y is
another recurring unit, where recurring unit Y is coupled to the
aromatic ring in an ortho, meta, or para relation to the imide
group.
39. A method of preparing a fluid separation membrane for
separating one or more components from a fluid, the fluid
comprising two or more components, comprising adding at least one
dithiolene to at least one polymer, the dithiolene having the
structure: 44where M is a metal, wherein R.sub.1, R.sub.2, R.sub.3,
and R.sub.4 are each independently alkyl, CH.sub.3, CF.sub.3,
C.sub.6H.sub.4OCH.sub.3, CN, or where R.sub.1 and R.sub.2 and/or
R.sub.3 and R.sub.4 combine to form at least one ring.
40-59. (Cancelled)
60. A method of separating one or more components from a fluid, the
fluid comprising two or more components, comprising bringing the
fluid stream into contact with a face of a fluid separation
membrane, the fluid separation membrane comprising at least one
polymer and at least one dithiolene having the structure: 45where M
is a metal, wherein R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are each
independently alkyl, CH.sub.3, CF.sub.3, C.sub.6H.sub.4OCH.sub.3,
CN, or where R.sub.1 and R.sub.2 and/or R.sub.3 and R.sub.4 combine
to form at least one ring.
61-80. (Cancelled)
81. An apparatus for separating one or more components from a
fluid, the fluid comprising two or more components, comprising: a
body; a fluid separation membrane disposed within the body, the
fluid separation membrane comprising at least one polymer and at
least one dithiolene having the structure: 46where M is a metal,
wherein R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are each
independently alkyl, CH.sub.3, CF.sub.3, C.sub.6H.sub.4OCH.sub.3,
CN, or where R.sub.1 and R.sub.2 and/or R.sub.3 and R.sub.4 combine
to form at least one ring; a fluid stream inlet coupled to the body
downstream from the fluid separation membrane; a first fluid stream
outlet positioned upstream from the fluid stream inlet and down
stream from the fluid separation membrane; and a second fluid
stream outlet positioned downstream from the fluid separation
membrane.
82-101. (Cancelled)
Description
PRIORITY CLAIM
[0001] This application claims priority to U.S. Provisional Patent
Application No. 60/463,008 entitled "DITHIOLENE FUNCTIONALIZED
POLYMER MEMBRANE FOR OLEFIN/PARAFFIN SEPARATION" filed Apr. 15,
2003, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to polymeric
membranes that exhibit gas selectivity. Specifically, rigid
polymeric membranes that exhibit an olefin/paraffin selectivity are
described.
[0004] 2. Description of the Related Art
[0005] The separation of one or more gases from a multicomponent
mixture of gases is necessary in a large number of industries. Such
separations currently are undertaken commercially by processes such
as cryogenics, pressure swing adsorption, and membrane separations.
In certain types of gas separations, membrane separations have been
found to be economically more viable than other processes.
[0006] In a pressure-driven gas membrane separation process, one
side of the gas separation membrane is contacted with a
multicomponent gas mixture. Certain of the gases of the mixture
permeate through the membrane faster than the other gases. Gas
separation membranes thereby allow some gases to permeate through
them while serving as a relative barrier to other gases. The
relative gas permeation rate through the membrane is a property of
the membrane material composition and its morphology.
[0007] It has been suggested in the prior art that the intrinsic
permeability of a polymer membrane is a function of both gas
diffusion through the membrane, controlled in part by the packing
and molecular free volume of the material, and gas solubility
within the material. Selectivity may be determined by the ratio of
the permeabilities of two gases being separated by a material.
[0008] Transport of gases in polymers and molecular sieve materials
occurs via a well known sorption-diffusion mechanism. The
permeability coefficient (P.sub.A) of a particular gas is the flux
(N.sub.A) normalized to the pressure difference across the membrane
(.DELTA.P.sub.A), and the membrane thickness (l). 1 P A = N A l p A
( 1 )
[0009] The permeability coefficient of a particular penetrant gas
is also equal to the product of the diffusion coefficient (D.sub.A)
and the solubility coefficient (S.sub.A).
P.sub.A=D.sub.AS.sub.A (2)
[0010] The permselectivity (.alpha..sub.A/B) of a membrane material
(also ideal selectivity) is the ratio of the permeability
coefficients of a penetrant pair for the case where the downstream
pressure is negligible relative to the upstream feed pressure.
Substituting equation (2), the ideal permselectivity is also a
product of the diffusivity selectivity and solubility selectivity
of the particular gas pair. 2 A / B = P A P B = D A D B S A S B ( 3
)
[0011] The variation of gas permeability with pressure in glassy
polymers is often represented by the dual mode model. Petropulos
(1970); Vieth, et al. (1976); Koros, et al. (1977). The model
accounts for the differences in gas transport properties in an
idealized Henry's law and Langmuir domains of a glassy polymer, 3 P
= k D D D + C H ' D H b 1 + bp ( 4 )
[0012] where k.sub.D is the Henry's law constant, C'.sub.H is the
Langmuir capacity constant, p is pressure, and b is the Langmuir
affinity constant. This model can be further extended to mixed gas
permeability: 4 P A = k DA D DA + C HA ' b A D HA 1 + b A p A + b B
p B ( 5 )
[0013] where p.sub.A and p.sub.B are the partial pressures of
gasses A and B respectively. This model is valid for a binary gas
mixture of components A and B, and it only accounts for competitive
sorption.
[0014] The temperature dependence of permeability for a given set
of feed partial pressures is typically represented by an Arrhenius
relationship: 5 P = P o exp [ - E p RT ] ( 6 )
[0015] where P.sub.o is a pre-exponential factor, E.sub.p is the
apparent activation energy for permeation, T is the temperature of
permeation in Kelvin, and R is the universal gas constant. The
permeability can further be broken up into temperature dependent
diffusion and sorption coefficients from equation (2). The
temperature dependence of the penetrant diffusion coefficient can
also be represented by an Arrhenius relationship: 6 D = D o exp [ -
E d RT ] ( 7 )
[0016] Again D.sub.o is a pre-exponential factor, and E.sub.d is
the activation energy for diffusion. The activation energy for
diffusion represents the energy required for a penetrant to diffuse
or "jump" from one equilibrium site within the matrix to another
equilibrium site. The activation energy is related to the size of
the penetrant, the rigidity of the polymer chain, as well as
polymeric chain packing. The temperature dependence of sorption in
polymers may be described using a thermodynamic van't Hoff
expression: 7 S = S o exp [ - H s RT ] ( 8 )
[0017] where S.sub.o is a pre-exponential factor, and H.sub.s is
the apparent heat of sorption as it combines the temperature
dependence of sorption in both the Henry's law and Langmuir
regions.
[0018] From transition state theory the pre-exponential for
diffusion can be represented by 8 D o = 2 kT h exp [ S d R ] ( 9
)
[0019] Here, S.sub.d is the activation entropy, .lambda. is the
diffusive jump length, k is Boltzmann's constant, and h is Planck's
constant. Substituting (9) into (3) (neglecting small differences
in the jump length of similarly sized penetrants) results in the
diffusive selectivity as the product of energetic and entropic
terms: 9 D A D B = exp [ - E d , A , B RT ] exp [ S d , A , B R ] (
10 )
[0020] The diffusivity selectivity is determined by the ability of
the polymer to discriminate between the penetrants on the basis of
their sizes and shapes, and is governed primarily by intrasegmental
motions and intersegmental packing. The diffusive selectivity will
be based on both the difference in activation energy for both
penetrants, .DELTA.E.sub.d, as well as the difference in activation
entropy for both penetrants, .DELTA.S.sub.d.
[0021] Much of the work in the field has been directed to
developing membranes that optimize the separation factor and total
flux of a given system. It is disclosed in U.S. Pat. No. 4,717,394
to Hayes that aromatic polyimides containing the residue of
alkylated aromatic diamines are useful in separating a variety of
gases. Moreover, it has been reported in the literature that other
polyimides, polycarbonates, polyurethanes, polysulfones and
polyphenyleneoxides are useful for like purposes. U.S. Pat. No.
5,599,380 to Koros, herein incorporated by reference, discloses a
polymeric membrane with a high entropic effect. U.S. Pat. No.
5,262,056 to Koros et al., herein incorporated by reference,
discloses polyamide and polypyrrolone membranes for fluid
separation.
[0022] U.S. Pat. No. 5,074,891 to Kohn et al. discloses certain
polyimides with the residuum of a diaryl fluorine-containing
diamine moiety as useful in separation processes involving, for
example, H.sub.2, N.sub.2, CH.sub.4, CO, CO.sub.2, He and O.sub.2.
By utilizing a more rigid repeat unit than a polyimide, however,
even greater permeability and permselectivity are realized. One
example of such a rigid repeat unit is a polypyrrolone.
[0023] Polypyrrolones as membrane materials were proposed and
studied originally for the reverse osmosis purification of water by
Scott et al. (1970). The syntheses, permeabilities, solubilities
and diffusivities of polypyrrolones and polyimides have been
described in (Walker and Koros (1991); Koros and Walker (1991); Kim
et al. (1988a, b); Kim (1988c); Coleman (1992)). Membranes that are
composed of the polyamide and polypyrrolone forms of
hexafluoroisopropylidene-bisphthalic anhydride are disclosed in
U.S. Pat. No. 5,262,056 which is incorporated herein by
reference.
[0024] In the petrochemical industry, one of the most important
processes is the separation of olefin and paraffin gases. Olefin
gases, particularly ethylene and propylene, are important chemical
feed stocks. Various petrochemical streams contain olefins and
other saturated hydrocarbons. These streams typically originate
from a catalytic cracking unit. Currently, the separation of olefin
and paraffin components is done using low temperature distillation.
Distillation columns are normally around 300 feet tall and contain
over 200 trays. This is extremely expensive and energy intensive
due to the similar volatilities of the components.
[0025] It is estimated that 1.2.times.10.sup.14 BTU per year are
used for olefin/paraffin separations. This large capital expense
and exorbitant energy cost have created incentive for extensive
research in this area of separations. Membrane separations have
been considered as an attractive alternative. Some examples of
membranes that exhibit attractive selectivity under mild conditions
have been reported. (Tanaka et al. (1996); Staudt-Bickel and Koros
(2000); Ilinitch et al. (1993); Lee et al. (1992); Ito et al.
(1989)). In practice, high propylene/propane temperatures and
pressures are preferred for economical processing. Thus, a polymer
membrane that showed enhanced propylene/propane selectivity under
increasingly demanding processing conditions would be of particular
value. Recent gas transport studies aimed at improving current
membrane performance have examined glassy polymers focusing mainly
on polyimides. Tanaka et al. (1996) have reported one of the
highest performance polyimides to date. This data along with other
literature data has been used to construct a preliminary
propane/propylene "upper bound" trade off curve between gas
permeability and selectivity, as shown in FIG. 1 (Tanaka et al.
(1996); Staudt-Bickel and Koros (2000); Ilinitch et al. (1993); Lee
et al. (1992); Ito et al. (1989); Steel (2000)). The conditions
chosen for the upper bound curve are 2-4 atm feed pressure and
35-55.degree. C. The propane/propylene trade off curve is less
defined at this point in comparison to O.sub.2/N.sub.2 and
CO.sub.2/CH.sub.4 "upper bound" curves defined previously (Robeson
(1991)).
[0026] According to Freeman's analysis, the "upper bound" for
conventional polymers used for gas separations can be shown to
follow equation 11:
.alpha..sub.A/B=(.beta..sub.A/B)/(P .sub.A.sup..lambda.A/B)
(11)
[0027] The parameter, .lambda..sub.A/B can be shown to be
proportional to the square of the size difference of the two gas
molecules, (dA/dB).sup.2. Consequently, this parameter is difficult
to manipulate through materials engineering. Therefore, according
to the theory, in order to "move" the upper bound limit, the
strategy must be to increase the .beta. parameter, which can be
shown to be proportional to the value, S.sub.A
(S.sub.A/S.sub.B).sup..lambda., as well as a parameter f, which
relates to the interchain spacing. Previous work has attempted to
increase the diffusivity selectivity through an increase in the
chain rigidity by using polypyrrolone materials. However, another
approach to "elevating" the upper bound is to improve the
solubility of the "fast gas" (i.e., C.sub.3H.sub.6 in this case),
thereby increasing the solubility selectivity, and increasing
.beta.. The solubility of an olefin in a polymeric material is a
parameter that can be engineered through the use of .pi.-bonding
interactions.
[0028] Previous researchers have examined the viability of fixed
site facilitated membranes for the separation of olefins from
paraffins. Typically, Group I-B metals, such as silver, are
dissolved in polymer membranes in a salt form. Examples of silver
salts conventionally used include AgBF.sub.4 and AgNO.sub.3. Once
dissolved in the polymer, the salt dissociates, and the silver
cation is able to form a complex with an olefin due to the
interaction of the .pi.-orbital of the olefin with the .sigma. and
.pi.-orbital of the metal.
[0029] These fixed site facilitated membranes still have a major
practical problem, however, due to the poor chemical stability of
the metal-olefin complex. This metal-olefin complex is easily
poisoned by small amounts of hydrogen gas, carbon monoxide,
acetylene, or hydrogen sulfide in the feed stream. Silver ions also
have the potential to react with acetylene to form an explosive
silver acetylide salt.
[0030] A search has been ongoing to find a material which can form
a .pi.-bond complex with olefins, while still maintaining stability
in the presence of the aforementioned impurity gases. An additional
constraint is that the material should be able to dissolve in
state-of-the-art polyimide membranes. The overall strategy is to
maintain the high diffusivity selectivity (D.sub.A/D.sub.B) already
available with polyimides, and enhance this diffusivity selectivity
by a factor of the improved solubility selectivity
(S.sub.A/S.sub.B). For a conventional polyimide with a
C.sub.3H.sub.6/C.sub.3H.sub.8 selectivity of 15, a small increase
in the solubility selectivity from 1.0 to 2.0 would double the
overall C.sub.3H.sub.6/C.sub.3H.sub.8 selectivity to a value of 30,
as well as doubling the C.sub.3H.sub.6 flux.
SUMMARY
[0031] Described herein is a polymeric fluid separation membrane.
In one embodiment, the fluid separation membrane may be formed from
the reaction product of a tetraacid compound and a diamine. The
initial resulting product is a polyamide. This polyamide may be
used to form a fluid separation membrane. The polyamide may be
thermally or chemically cyclized to form a polyimide. The polymer
matrix of the fluid separation membrane may also include a
dithiolene.
[0032] In an embodiment where dithiolenes are included within the
polymer matrix, rigid polymeric membranes that exhibit an
olefin/paraffin solubility selectivity may result. Dithiolenes may
be added to a polymer formed by reacting a tetraacid compound with
a diamine, a tetraamine, or a mixture of diamines and tetraamines.
Dithiolenes may be added to any polymer matrix such that the
dithiolenes are substantially homogeneously dispersed within the
polymer matrix.
[0033] The fluid separation membrane may be formed by adding a
tetraacid compound to an amine mixture. The amine mixture may
include tetraamines and diamines. The tetraamine to diamine ratio
may be between about 5:95 to about 100:0. After the tetraacid
compound and the amines are reacted, the resulting polyamide may be
filtered, washed and dried. The polyamide may be converted to a
polyimide by heating the polyamide to a temperature above about
200.degree. C. Either the polyamide or the polyimide may be used in
a fluid separation membrane. In an embodiment, a dithiolene may be
added to a polymer during a film casting process. The solvent may
be removed from the resulting dithiolene polymer solution to
provide a polymer film that has a dithiolene incorporated within
the polymer.
[0034] The above-described fluid separation membranes may be used
in any fluid separation apparatus known in the art. Generally, a
fluid separation apparatus includes a body in which a fluid
separation membrane is disposed. A fluid inlet may be positioned
downstream from the fluid separation membrane. Two fluid outlets
may be positioned upstream from the fluid inlet. A first fluid
outlet may be positioned downstream from the fluid separation
membrane. A second fluid separation membrane may be positioned
upstream or downstream from the fluid separation membrane.
[0035] During use, a fluid stream that includes at least two
components (e.g., a gas stream) may be introduced into the fluid
separation apparatus via the fluid separation inlet. The fluid will
then contact the fluid separation membrane. The fluid separation
membrane may have a differential selectivity such that one of the
components in the gas stream may pass through the fluid separation
membrane at a rate that is faster than the rate at which the other
component passes through. The faster permeating component passes
through the gas separation membrane and flow out of the fluid
separation apparatus via a fluid outlet. The gas that does not
permeate through the membrane may exit the fluid separation
apparatus via another fluid outlet. The fluid stream passing out of
the fluid outlet upstream from the membrane may be recycled back
into the fluid separation apparatus to improve the separation of
the components and to maximize the yield of purified
components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Advantages of the present invention may become apparent to
those skilled in the art with the benefit of the following detailed
description of the preferred embodiments and upon reference to the
accompanying drawings in which:
[0037] FIG. 1 depicts a C.sub.3H.sub.6/C.sub.3H.sub.8 upperbound
tradeoff curve, based on available literature data.
[0038] FIG. 2 depicts a fluid separation apparatus.
[0039] FIG. 3 depicts penetrant sorption in polymer films.
[0040] FIG. 4 depicts a comparison of C.sub.3H.sub.6/C.sub.3H.sub.8
solubility selectivity for 6FDA-6FpDA polyimide with dithiolene
additive.
[0041] FIG. 5 depicts difference in C.sub.3H.sub.6/C.sub.3H.sub.8
concentration due to dithiolene additive.
[0042] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof are shown by
way of example in the drawings and may herein be described in
detail. The drawings may not be to scale. It should be understood,
however, that the drawings and detailed description thereto are not
intended to limit the invention to the particular form disclosed,
but on the contrary, the intention is to cover all modifications,
equivalents and alternatives falling within the spirit and scope of
the present invention as defined by the appended claims.
DETAILED DESCRIPTION
[0043] Polyimide and poly (pyrrolone-imide) polymers are polymers
derived from the condensation reaction of a tetraacid compound, a
diamine and possibly a tetraamine. The resulting product is a
polyamide. The remaining functional groups are then reacted during
a thermal curing step to form the polyimide or poly
(pyrrolone-imide). The polymerization may be conducted in an
aprotic polar solvent capable of dissolving the monomers.
[0044] Tetraacid compounds, as used herein, include compounds that
include at least four carboxylic acid groups and compounds that are
derivatives of such compounds. Examples of tetraacid compounds
include tetraacids, dianhydrides, and bis-ortho-ester-acid halides.
Preferably, the tetraacid compound is an aromatic tetraacid or an
aromatic tetraacid derivative. Aromatic tetraacid compounds tend to
produce a rigid, thermally stable, productive and selective
membrane material.
[0045] Tetraacids may be used to form the polyamide precursor
polymer. The acid groups, in some embodiments, may be paired into
ortho pairs that are separated by at least three atoms as shown in
structures (1-3) below. The simplest compound to meet these
requirements would be 1,2,4,5-benzene tetracarboxylic acid, shown
as (1). The two ortho pairs are the 1,2 pair and the 4,5 pair, and
three atoms lie between the carbons of the acid groups of non-ortho
pairs. Other compounds include pyridine tetraacids (e.g., structure
(2)) and pyrazine tetraacids (e.g., structure (3)). 1
[0046] Tetraacids, however, may lack the reactivity to produce high
molecular weight polymer. One way to increase the reactivity of the
tetraacid compound is to convert the tetraacid into a dianhydride.
Dianhydrides may be prepared from the corresponding tetraacids by
heating to 230.degree. C. in a vacuum or by refluxing the tetraacid
with acetic anhydride. Examples of dianhydrides are shown as
structures (4)-(6). The dianhydrides shown (4)-(6) are the
dianhydrides that would be derived from the tetraacids (1)-(3)
respectively. 2
[0047] Naphthalene tetraacid derivatives may also be used.
Naphthalene derivatives include carboxylic acid groups that may be
either ortho-paired or para-paired. Naphthalene tetraacid
derivatives include compounds having the general structure (7).
3
[0048] Ortho-paired and para-paired derivatives include compounds
in which at least one of the pairs: R.sub.1 and R.sub.2; R.sub.2
and R.sub.3; R.sub.3 and R.sub.4; R.sub.1 and R.sub.8; and R.sub.1
and R.sub.4 is a pair of carboxylic acid groups; and at least one
of the pairs: R.sub.5 and R.sub.6; R.sub.6 and R.sub.7; R.sub.7 and
R.sub.8; R.sub.4 and R.sub.5; and R.sub.5 and R.sub.8 is a pair of
carboxylic acid groups. An example of a para-paired naphthalene
type monomer would be 1,4,5,8-naphthalene tetracarboxylic acid.
Ortho-paired naphthalene tetraacid derivatives include
1,2,5,6-naphthalene tetracarboxylic acid (8) and
2,3,6,7-naphthalene tetracarboxylic acid (9). 4
[0049] Naphthalene dianhydrides may also be used. Naphthalene
dianhydrides may be prepared from the corresponding tetraacids by
heating to 230.degree. C. in a vacuum or by refluxing the tetraacid
with acetic anhydride. Examples of naphthalene dianhydrides are
shown as structures (10) and (11) which correspond to the
dianhydrides that would be derived from the naphthalene
tetracarboxylic acids (8) and (9) respectively. 5
[0050] Other tetraacids may include aromatic
bis-(ortho-dicarboxylic acids) and aromatic bis-(ortho-di-acid
anhydrides). Generally, these compounds include a bis aromatic
structure to which carboxylic acids and/or anhydrides are attached.
Examples of these compounds include aromatic
bis-(ortho-dicarboxylic acids) (12) and aromatic bis-(ortho-di-acid
anhydrides) (13). 6
[0051] where X is a suitable linking group. Examples of linking
groups include elemental linkages such as NH, O, or S. Other groups
include CH.sub.2, C(O), CH(CH.sub.3), C(CH.sub.3).sub.2,
C(CF.sub.3).sub.2, C(CH.sub.3)Ph, C(Ph).sub.2, cyclohexyl,
sulfoxide, sulfonate. A specific example of a compound having
general structure (13), where X is C(CF.sub.3).sub.2, is
4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA). Other
linking groups may include compounds having the structures
(14)-(17). 7
[0052] where Y is any of the other linking groups X. Alternatively,
the linking group, X may represent a direct connection between the
two aromatic groups such as depicted for the dianhydride (18).
8
[0053] Another reactive tetraacid derivative is an acid chloride
derivative. This type of compound may be prepared from any of the
above described dianhydrides by reaction with an alcohol to form a
bis-(ortho-acid-ester) followed by reaction to convert acid groups
to acid halides. This method prepares a very reactive monomer, but
this reactivity makes the monomer more water sensitive.
Additionally, larger, more slowly diffusive side product alcohol
groups are given off during the final cure of the polyamide to the
polypyrrolone. With either the dianhydride or bis-ortho-ester-acid
halide, preferably chloride, the functionality of the monomer is
two, leading to linear polymer formation.
[0054] Tetraamines, as used herein, include compounds that include
at least four amine groups. Preferably the tetraamine is an
aromatic tetraamine. Aromatic tetraamine compounds tend to produce
a rigid, thermally stable, productive and selective membrane
material.
[0055] Tetraamines may be used to form the polyamide precursor
polymer. The amine groups, in some embodiments, may be paired into
ortho pairs that are separated by at least three atoms as shown in
structures (18-20) below. The simplest compound to meet these
requirements would be 1,2,4,5-tetraminobenzene (TAB), shown as
(18). The two ortho pairs are the 1,2 pair and the 4,5 pair, and
three atoms lie between the carbons of the acid groups of non-ortho
pairs. Other compounds include pyridine tetraacids (e.g., structure
(19)) and pyrazine tetraacids (e.g., structure (20)). 9
[0056] Naphthalene tetraamines may also be used. Naphthalene
tetraamines include amine groups that may be either ortho-paired or
para-paired. Naphthalene tetraamine derivatives include compounds
having the general structure (21). 10
[0057] Ortho-paired and para-paired derivatives include compounds
in which at least one of the pairs: R.sub.1 and R.sub.2; R.sub.2
and R.sub.3; R.sub.3 and R.sub.4; R.sub.1 and R.sub.8; and R.sub.1
and R.sub.4 is a pair of amine groups; and at least one of the
pairs: R.sub.5 and R.sub.6; R.sub.6 and R.sub.7; R.sub.7 and
R.sub.8; R.sub.4 and R.sub.5; and R.sub.5 and R.sub.8 is a pair of
amine groups. An example of a para-paired naphthalene type monomer
would be 1,4,5,8-tetraminonaphthalen- e (22). Ortho-paired
naphthalene tetraamines include 1,2,5,6-tetraminonaphthalene (23)
and 2,3,6,7-tetraaminonaphthalene (24). 11
[0058] Other tetraacids may include aromatic bis-(ortho-diamines)
(25). Generally, these compounds include a bis aromatic structure
with amines attached to the aromatic groups. The linking group, X,
may be the same as described above for the tetraacid derivatives.
12
[0059] Other fused ring systems such as fluorene (26) and
tetramethyl-spiro-biindane (27) may also serve as substrates for
tetraamines (as depicted) or tetracarboxylic acid derivatives.
However, all four of the acid or amino groups need not be attached
to different ring, provided the four are split into ortho-pairs or
para-pairs. 13
[0060] The tetraamines may be obtained either commercially, or by
the reduction of a nitro compound, or may be synthesized in three
steps from a bisphenol. The method for synthesis of tetraamine from
bisphenol involves the nitration of the bisphenol, the nucleophilic
exchange of the hydroxyl groups for amino groups, and reduction of
the amino groups. The exchange of the hydroxyl groups for amino
groups is similar to the procedure described in U.S. Pat. No.
2,894,988, which is incorporated herein by reference, for the
conversion of nitro-cresols to nitro-toluidines.
Spirobiindane-bisphenol, which serves as a basis for useful gas
separating polycarbonates, can thus be converted to a tetraamine
(12) for polypyrrolone synthesis of fluid separation materials. The
synthesis of other tetraamines and tetraacids is described in U.S.
Pat. No. 5,262,056 to Koros et al. which is incorporated herein by
reference.
[0061] Diamines are, generally, molecules that include at least two
amine groups. In one embodiment, aromatic diamines may be used.
Aromatic diamines may be benzene based (28) or naphthalene based
(29). 14
[0062] where, for benzene derivatives, meta or parasubstituted
diamines may be used. As depicted in structure (28) R.sub.1 and
either R.sub.3 or R.sub.4 may be NH.sub.2, where the remaining
pendant groups are H or a C.sub.1 to C.sub.12 hydrocarbon. For
naphthalene derivatives, at least two of R.sub.1, R.sub.2, R.sub.3,
R.sub.4, R.sub.5, R.sub.6, R.sub.7, and R.sub.8 are NH.sub.2 with
the NH.sub.2 groups being in an meta- or para orientation, the
remaining pendant groups are H or a C.sub.1 to C.sub.12
hydrocarbon. Specific examples of aromatic diamines include
2,4,6-trimethyl-1,3-phenylenediamine (DAM).
[0063] Other diamines may include bis-aromatic amines (41).
Generally, these compounds include a bis aromatic structure
with-amines attached to the aromatic groups. The linking group, X,
may be the same as described above for the tetraacid derivatives.
15
[0064] Specific examples of bis-aromatic amines include, but are
not limited to, 4,4' (hexafluoroisopropylidene) dianiline (6FpDA)
and 3,3'-dimethyl-4,4'-diaminophenyl (3,3'DMDB).
[0065] In one embodiment, a fluid separation membrane may be
synthesized by the reaction of a tetraacid compound with an amine
mixture that includes tetraamines and diamines. Polyimides are
condensation polymers obtained from the reaction of aromatic
dianhydrides with diamines followed by complete cyclization.
Polypyrrolones are condensation polymers obtained from the reaction
of aromatic dianhydrides and aromatic tetraamines followed by
complete cyclization. The polymer obtained by the initial reaction
of the monomers in an aprotic solvent is a soluble poly(amide amino
acid), which can be thermally cyclized to form a polypyrrolone. A
poly (pyrrolone-imide) may be synthesized in a similar manner.
Initially a tetraacid compound is reacted with an amine mixture
that includes tetraamines and diamines. In one embodiment the ratio
of tetraamine to diamine in the amine mixture may be between about
5:95 to about 100:0. A small excess of the tetraacid compound may
be used. Both the tetraamines and diamines condense with the
tetraacid compound to form a polyamide. The polyamide may be
thermally cyclized to form the poly (pyrrolone-imide). Thermal
cyclization of an amide formed between the tetraacid compound and
the tetraamine will lead to a pyrrolone linkage, while thermal
cyclization of an amide formed between the tetraacid compound and
the diamine will lead to imide linkages. The reaction of the
tetraacid compound and the amine mixture may be performed in a
polar aprotic solvent. Aprotic solvents, generally, are solvents
that neither donate or accept protons. Examples of polar aprotic
solvents include, but are not limited to dimethylformamide,
n-methyl pyrrolidinone, dimethylacetamide, and dimethyl sulfoxide.
One or all of the components may be dissolved in a polar aprotic
solvent prior to reacting the components.
[0066] A base may be added to catalyze the formation of the
polyamide. In an embodiment, a tertiary amine may be added to the
amine mixture prior to the addition of the tetraacid compound.
Suitable tertiary bases include, but are not limited to pyridine,
pyrazine, triethylamine, diisopropyl ethyl amine,
1,5-diazabicyclo[4.3.0]non-5-ene ("DBN"),
1,4-diazabicyclo[2.2.2]octane,
1,8-diazabicyclo[5.4.0]undec-7-ene.
[0067] In one embodiment, the amine mixture may be dissolved in a
polar aprotic solvent and placed in a reaction vessel. The
tetraacid derivative may also be dissolved in a polar aprotic
solvent and added to the amine mixture. The reaction may be
conducted under an oxygen free atmosphere. An oxygen free
atmosphere may be obtained by replacement of the ambient air in the
reaction vessels with an inert gas such as helium, nitrogen, or a
nobel gas (e.g., argon). Generally, the addition of the tetraacid
compound to the amine mixture may cause an exothermic condensation
reaction to occur. The rate of addition of the tetraacid derivative
may be adjusted to control the temperature of the reaction. The
resulting polyamide may be collected, filtered and dried to remove
unreacted monomers and any base that may be present.
[0068] To convert the polyamide to a poly (pyrrolone-imide) the
polyamide may be heated to cause further condensation of the
amides. Condensation of the resulting amide may lead to either
pyrrolone or imide linking groups. Thermal cyclocondensation may
occur at temperatures above about 200.degree. C. In one embodiment,
the polyamide may be placed in a mold prior to thermal
cyclocondensation such that the resulting poly (pyrrolone-imide)
polymer has a shape that is complementary to the shape of the mold.
The polyamide may be heated under an inert atmosphere or at a
pressure below about 1.0 mmHg. Performing a thermal
cyclocondensation under a vacuum may help to remove water formed
during the condensation reaction and help accelerate the reaction
rate. Thermal cyclocondensation is performed for a period of at
least about one day, preferably two to three days. The
polypyrrolone resulting from cyclization possesses a repeat unit
with two benzene rings joined by two fused five membered rings,
imparting a great degree of thermal and chemical resistance,
strength and rigidity.
[0069] Either a polyimide, a polyamide or the poly
(pyrrolone-imide) may be used as fluid separation membranes.
Methods for forming and testing fluid separation membranes are
described in detail in U.S. Pat. Nos. 5,262,056 and 6,602,415, both
to Koros which are both incorporated herein by reference. The
membranes of the present invention may be either composite or
asymmetric membranes.
[0070] The above-described fluid separation membranes may be used
in any fluid separation apparatus known in the art. A schematic of
a fluid separation membrane is depicted in FIG. 2. Generally, a
fluid separation apparatus 200 includes a body 202 in which a fluid
separation membrane 204 is disposed. The fluid separation membrane
202 may be composed of any of the polymers described herein and
formed by the methods described herein. A fluid inlet may be
positioned downstream from the fluid separation membrane 204. Two
fluid outlets may be positioned upstream from the fluid inlet. A
first fluid outlet 206 may be positioned upstream from the fluid
separation membrane. A second fluid separation membrane may be
positioned upstream from the fluid separation membrane.
[0071] During use, a fluid stream that includes at least two
components (e.g., a gas stream) may be introduced into the fluid
separation apparatus 200 via the fluid separation inlet. The fluid
will then contact the fluid separation membrane 204. The fluid
separation membrane may have a differential selectivity such that
one of the components in the gas stream may pass through the fluid
separation membrane at a rate that is faster than the rate at which
the other component passes through. Thus the faster permeating
component will pass through the gas separation membrane and flow
out of the fluid separation apparatus via an outlet. The gas that
does not permeate through the membrane may exit the fluid
separation apparatus via the outlet 206. The fluid stream passing
out of the outlet 206 may be recycled back into the fluid
separation apparatus to improve the separation of the components
and to maximize the yield of purified components.
[0072] In an embodiment, dithiolenes may be added to a polymer
mixture. The polymer may be formed as described herein. In an
embodiment, the polymer may be formed by reacting a tetraacid and a
diamine; a tetraacid and a tetraamine, or a tetraacid with a
mixture of a tetraamine and a diamine. The polymer may be any
polymer suitable to allow a particular dithiolene to be
homogeneously dispersed. It may be necessary to use different
polymers for different dithiolenes. The dithiolenes may be
homogeneously dispersed within the polymer matrix. The resulting
polymer dithiolene product may be used to form a fluid separation
membrane as described herein. Addition of the dithiolene may
increase the solubility selectivity of a fluid separation membrane.
In an embodiment, a fluid separation membrane including dithiolenes
may exhibit an olefin/paraffin solubility selectivity. A fluid
separation membrane including dithiolenes may exhibit
olefin/paraffin solubility selectivity of between about 1.1 to
about 2.0. It is believed that the solubility selectivity of the
membranes that incorporate dithiolene may be due to the ability of
dithiolenes to reversibly complex with an olefin. The dithiolene
may be resistant to poisoning by impurities. Poisoning within the
context herein refers to decreasing the effectiveness of a compound
or material as regards its intended purpose. Impurities may include
any common impurities found in fluid streams that come into contact
with a fluid separation membrane containing a dithiolene
additive.
[0073] In an embodiment, the dithiolene may have the general
structure (30): 16
[0074] where M is a metal. Metals may include, but are not limited
to nickel, platinum, and palladium. R.sub.1, R.sub.2, R.sub.3, and
R.sub.4 may be each independently alkyl, H, CH.sub.3, CF.sub.3,
C.sub.6H.sub.4OCH.sub.3, CN, or aryl. R.sub.1 and R.sub.2 and/or
R.sub.3 and R.sub.4 may combine to form at least one ring. The ring
may be aromatic or nonaromatic. The ring may be substituted or
nonsubstituted. Dithiolene (30) may be symmetric or asymmetric. In
a particular example, R.sub.1 and R.sub.2 and R.sub.3 and R.sub.4
may combine to form substituted aromatic rings forming an overall
asymmetric dithiolene (30). An asymmetric dithiolene may be a
mixture of stereoisomers.
[0075] In an embodiment, dithiolene (30) may include a valence
charge. The valence charge may be, for example, -1, or -2.
Dithiolene (30) may include a counter ion. A counter ion may
include any suitable counter ion known to one skilled in the art. A
counter ion may be chosen for a number of different reasons based
on what properties may be needed. For example, a counter ion may be
chosen to increase the solubility of the entire complex. In one
embodiment, the counter ion may have the structure (31): 17
[0076] where each R is independently an alkyl or aromatic compound.
In one embodiment, each R may be independently C.sub.2H.sub.5 or
C.sub.4H.sub.9.
[0077] In an embodiment, dithiolene may have structure (32): 18
[0078] which is similar to structure (30), where R.sub.1, R.sub.2,
R.sub.3, and R.sub.4 are CF.sub.3. M is a metal such as nickel,
platinum, or palladium.
[0079] In an embodiment, dithiolene may have structure (33): 19
[0080] which is similar to structure (30), where R.sub.1, R.sub.2,
R.sub.3, and R.sub.4 are CF.sub.3. M is a metal such as nickel,
platinum, or palladium.
[0081] In an embodiment, R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are
C.sub.6H.sub.4OCH.sub.3. Each OCH.sub.3 substituent separately may
be positioned anywhere on the aromatic ring. In one embodiment,
dithiolene may have structure (34): 20
[0082] which is similar to structure (30), where R.sub.1, R.sub.2,
R.sub.3, and R.sub.4 are C.sub.6H.sub.4OCH.sub.3, with the methoxy
substituent in the para position as depicted. M is a metal such as
nickel, platinum, or palladium.
[0083] In an embodiment, dithiolene may have structure 35: 21
[0084] which is similar to structure 30, where R.sub.1 and R.sub.2,
and R.sub.3 and R.sub.4 may combine to form a substituted aromatic
ring. M is a metal such as nickel, platinum, or palladium.
[0085] In an embodiment, dithiolene has the structure 36: 22
[0086] where R.sub.1 and R.sub.2 combine to form
C.sub.6H.sub.4S.sub.4, and R.sub.3 and R.sub.4 are CF.sub.3. M is a
metal such as nickel, platinum, or palladium.
[0087] A dithiolene may be dispersed in a polymer matrix as
described herein. In an embodiment, a dithiolene may be dispersed
in a polymer resulting from at least the reaction of a tretraacid
and a diamine. The tetraacid may be dianhydrides such as (37)
and/or (38): 23
[0088] The diamine may have the structure (39): 24
[0089] X may be, but is not limited to, a linking group such as
CH.sub.2, C(O), CH(CH.sub.3), C(CH.sub.3).sub.2, C(CF.sub.3).sub.2,
C(CH.sub.3)Ph, C(Ph).sub.2, or cyclohexyl. A polymer matrix may be
a polyimide polymer, a polyamide polymer, a polypyrrolone polymer,
and/or a poly (pyrrolone-imide) polymer. A polyimide polymer may
include recurring units having the structure (40): 25
[0090] X may be a linking group. Y may be another recurring unit.
Recurring unit Y may be coupled to the aromatic ring in an ortho,
meta, or para relation to the imide group.
EXAMPLES
Synthesis Procedure of 6FDA-6FpDA
[0091] All monomer materials were purified before the
polymerization reaction. The 6FDA dianhydride and the 6FpDA diamine
were each sublimed twice. The monomers were stored separately under
high vacuum. For the synthesis of the polyimides in this study,
chemical imidization was performed. In a moisture free flask with
nitrogen inlet and magnetic stirrer, the diamine monomer was
dissolved in N,N-dimethyl acetamide (DMAc) and the 6FDA dianhydride
dissolved in DMAc was added dropwise at room temperature. The 20-25
wt % solution was stirred 6-8 h. Thereby high molecular polyamic
acids were formed. The imidization was performed by the dehydration
of the polyamic acids by adding a large excess of triethylamine and
acetic anhydride to the reaction mixture and stirring 2-3 h at 323
K and 10-20 min at 373-383 K. After cooling to room temperature,
the highly viscous reaction solution was slowly poured into
methanol. The precipitated polyimide was homogenized in a blender;
filtered and washed several times with fresh methanol. The obtained
polyimide was dried 12 h under vacuum at room temperature and at
least 24 h under vacuum at 523 K.
FILM CASTING TECHNIQUES
[0092] Films of the polymer materials were cast in a conventional
manner in a fume hood. The appropriate amount of polymer was
dissolved in a suitable solvent to form a 1-2 wt % solution. This
solution was stirred for at least 20 minutes before filtering the
solution with a 0.2 micron TEFLON syringe filter or alternatively
filter paper from Fischer Scientific with medium porosity. The
filtered solution was dispensed on a clean, level TEFLON dish or
glass plate. The film was covered with a casting funnel to control
the rate of solvent removal, and film formation generally occurred
in under 8 hours. The films were then removed and placed in the
vacuum oven at 100.degree. C. for at least 24 hours to ensure
complete solvent removal.
DITHIOLENE EXPERIMENTAL
[0093] A list of dithiolenes and their structures are presented in
Table 1. In one experiment, the nine dithiolene complexes listed in
Table 1, were evaluated for their reaction with C.sub.3H.sub.6.
Experiments were conducted that included bubbling low pressure
(e.g., atmospheric) C.sub.3H.sub.6 through a solution of the
dithiolene complex in question. The results of these experiments
are shown in Table 2. Some of the complexes were not soluble in
toluene, but were soluble in dimethylacetamide. The goal of the
experiment was to observe a color change over time, which would
signal a chemical complexation with propylene. The only dithiolene
material that underwent a significant change was complex #2,
Ni[S.sub.2C.sub.2(CF.sub.3).sub.2].sub.2, and this occurred in
under 30 minutes. All other dithiolenes showed no color change
under C.sub.3H.sub.6 bubbling, with the exception of dithiolene #5.
This complex underwent a slight color change from yellow to light
orange. The assumption from this would be that the olefin binding
is very weak, as it appears the energy (reflected in the color) is
not changed appreciably.
1TABLE 1 Chemical Formula of dithiolene materials tested. #
Chemical Formula 1 Ni[S.sub.2C.sub.2(CH.sub.3).sub.2].sub.2 2
Ni[S.sub.2C.sub.2(CF.su- b.3).sub.2].sub.2 3
Ni[S.sub.2C.sub.2(C.sub.6H.sub.4OCH.sub.3).sub.- 2].sub.2 4
[C.sub.6H.sub.4S.sub.4]{Ni[S.sub.2C.sub.2(CF.sub.3).sub.- 2]}.sup.-
5 [N(n-C.sub.4H.sub.9).sub.4]{Ni[S.sub.2C.sub.2(CN).sub.2-
].sub.2}.sup.- 6
[N(n-C.sub.4H.sub.9).sub.4]{Ni[S.sub.2(C.sub.6H.su-
b.3CH.sub.3)].sub.2}.sup.- 7
[N(n-C.sub.4H.sub.9).sub.4]{Pt[S.sub.2-
(C.sub.6H.sub.3CH.sub.3)].sub.2}.sup.- 8
[N(n-C.sub.4H.sub.9).sub.4-
]{Fe[S.sub.2(C.sub.6H.sub.3CH.sub.3)].sub.2}.sup.- 9
[N(C.sub.2H.sub.5).sub.4]{Co[S.sub.2(C.sub.2(CN).sub.2].sub.2}.sup.-
[0094]
2TABLE 2 Results of C.sub.3H.sub.6 bubbling experiments for the 9
dithiolene samples examined. Dithiolene Time of C.sub.3H.sub.6
Complex Solvent Color bubbling Color change #1 Toluene deep purple
3 hrs No change #2 Toluene dark with purple 30 minutes yellowish -
tint green #3 Toluene dark forest green 3 hrs No change #4 Toluene
light yellow 3 hrs No change #5 DMAc yellow 3 hrs light orange
(very slight change) #6 Toluene green with blue 3 hrs No change
tint #7 Toluene light blue 3 hrs No change #8 DMAc light red 3 hrs
No change #9 DMAc yellow 3 hrs No change
[0095] 26
[0096] Depicted above is the proposed method of complexation of
propylene with a dithiolene. The observation that
Ni[S.sub.2C.sub.2(CF.sub.3).sub.2- ].sub.2 undergoes complexation
with C.sub.3H.sub.6 is consistent with previous experiments in the
literature.
[0097] In one embodiment, a film was prepared using 6FDA-6FpDA
polyimide as the polymer matrix. The polyimide 6FDA-6FpDA was
synthesized from a mixture of 6FDA and 6FpDA using the general
methods described herein. It is believed that the presence of
CF.sub.3 groups in both the polymer and the dithiolene complex,
Ni[S.sub.2C.sub.2(CF.sub.3).sub.2].sub.2 should aid in miscibility
of the polymer and the dithiolene. Films were cast from a mixture
of 6FDA-6FpDA polymer and dithiolene on Teflon plates using
techniques described herein with dicloromethane as the casting
solvent. The films were then dried at 120.degree. C. for at least 8
hours under vacuum. Homogenous films were formed that were also
transparent dark green in epoxy on aluminum tape, compared to the
pure 6FDA-6FpDA film, which is clear. After successfully achieving
a polyimide/dithiolene homogenous blend,
C.sub.3H.sub.6/C.sub.3H.sub.8 pure gas permeation and sorption
experiments were conducted using the material
6FDA-6FpDA/Ni[S.sub.2C.sub.2(CF.sub.3).sub.2].sub.2 (11 wt %).
TRANSPORT RESULTS
C.sub.3H.sub.6/C.sub.3H.sub.8 Solubility Results
[0098] Initially pure gas C.sub.3H.sub.6/C.sub.3H.sub.8 sorption
experiments were conducted for both the pure polymer, 6FDA-6FpDA,
and the 6FDA-6FpDA/Ni[S.sub.2C.sub.2(CF.sub.3).sub.2].sub.2 (11 wt
%) blend, both processed using the same protocol. The results are
shown in FIG. 3 on a plot of gas concentration versus equilibrium
feed pressure. FIG. 3 depicts penetrant sorption in polymer films
at 35.degree. C. for C.sub.3H.sub.6 in
6FDA-6FpDA/Ni[S.sub.2C.sub.2(CF.sub.3).sub.2].sub.2 302,
C.sub.3H.sub.6 in 6FDA-6FpDA 300, C.sub.3H.sub.8 in 6FDA-6FpDA 304,
C.sub.3H6 in 6FDA-6FpDA/Ni[S.sub.2C.sub.2(CF.sub.3).sub.2].sub.2
306. These results were fit to the dual mode model describing gas
sorption in both a Langmuir environment and a Henry's law
environment:
S=(c/p)=k.sub.D+[(C'.sub.Hb)/(1+bp)] (13)
[0099] where k.sub.D is the Henry's law constant, C'.sub.H is the
Langmuir capacity constant, and b is the Langmuir affinity
constant. The sorption isotherms are shown in FIG. 3. The results
of the fitted parameters are shown in Table 3.
[0100] As shown in Table 3 there is a significant increase in b,
the affinity constant, for C.sub.3H.sub.6 in the dithiolene
containing material. Furthermore, there is also an increase in the
Henry's law constant, k.sub.D, for C.sub.3H.sub.6 within the
material 6FDA-6FpDA/Ni[S.sub.2C.sub.2(CF.sub.3).sub.2].sub.2,
compared to the pure polyimide.
[0101] It would be expected that the C'.sub.H parameter would
increase for C.sub.3H.sub.6 in the dithiolene-containing blend, and
that C'.sub.H for C.sub.3H.sub.8 would remain relatively constant.
Surprisingly, this is not what is observed. In both cases,
(C.sub.3H.sub.6 and C.sub.3H.sub.8) the C'.sub.H parameter is
depressed. This suggests that the dithiolene works to decrease the
available defect free volume within the matrix. One possibility is
that the dithiolene acts somewhat as a plasticizer, depressing the
Tg of the matrix. Previous studies have shown correlations between
the matrix Tg, and the C'.sub.H parameter.
[0102] Using the dual mode data, it is possible to plot the pure
gas C.sub.3H.sub.6/C.sub.3H.sub.8 solubility selectivity as a
function of feed pressure for each of the materials studied (FIG.
4). As shown in FIG. 4, the solubility selectivity is improved at
all pressures over the range studied. Line 400 depicts the
solubility selectivity for 6FDA-6FpDA/dithiolene #2 (11%) in FIG.
4. Line 402 depicts the solubility selectivity for 6FDA-6FpDA in
FIG. 4. The increase in the C.sub.3H.sub.6 affinity constant, b,
provides a large increase in the overall solubility selectivity at
low pressures. The increase in the C.sub.3H.sub.6 Henry's law
constant maintains an increase in the solubility selectivity at
higher pressures.
3TABLE 3 Dual mode parameters for C.sub.3H.sub.6/C.sub.3H.sub.8 in
6FDA-6FpDA and 6FDA-6FpDA/Ni[S.sub.2C.sub.2(CF.sub.3).sub.2].sub.2.
kD C'.sub.H Membrane cc (STP)/cc cc (STP)/cc b Material Gas polymer
- psia polymer psia-1 6FDA-6FpDA C.sub.3H.sub.6 0.32 26.4 0.14
6FDA-6FpDA/ C.sub.3H.sub.6 0.40 17.2 0.70
Ni[S.sub.2C.sub.2(CF.sub.3).sub.2].sub.2 6FDA-6FpDA C.sub.3H.sub.8
0.36 14.6 -- 6FDA-6FpDA/ C.sub.3H.sub.8 0.34 9.9 0.37
Ni[S.sub.2C.sub.2(CF.sub.3).sub.2].sub.2
[0103] FIG. 5 illustrates the difference in
C.sub.3H.sub.6/C.sub.3H.sub.8 concentration due to the dithiolene
additive. Concentration difference 502 increases with increased
pressure, which is believed to indicate that the olefin is able to
"access" more dithiolene molecules as the concentration increases
in the polymer. Upper limit 500 represents the calculated maximum
enhancement based on a mole balance assuming all dithiolene
molecules form a complex. The experimental measurements approach
this value as the pressure is increased.
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[0137] In this patent, certain U.S. patents, U.S. patent
applications, and other materials (e.g., articles) have been
incorporated by reference. The text of such U.S. patents, U.S.
patent applications, and other materials is, however, only
incorporated by reference to the extent that no conflict exists
between such text and the other statements and drawings set forth
herein. In the event of such conflict, then any such conflicting
text in such incorporated by reference U.S. patents, U.S. patent
applications, and other materials is specifically not incorporated
by reference in this patent.
[0138] Further modifications and alternative embodiments of various
aspects of the invention will be apparent to those skilled in the
art in view of this description. Accordingly, this description is
to be construed as illustrative only and is for the purpose of
teaching those skilled in the art the general manner of carrying
out the invention. It is to be understood that the forms of the
invention shown and described herein are to be taken as the
presently preferred embodiments. Elements and materials may be
substituted for those illustrated and described herein, parts and
processes may be reversed, and certain features of the invention
may be utilized independently, all as would be apparent to one
skilled in the art after having the benefit of this description of
the invention. Changes may be made in the elements described herein
without departing from the spirit and scope of the invention as
described in the following claims.
* * * * *